Recently, public attention has been directed to a coating powder comprising, as principal ingredients, a polyester resin and a crosslinking agent, as a pollution-free coating composition capable of producing a coating which is excellent in corrosion resistance, chemical resistance, mechanical strength and adhesion to steel or the like. Usually, a blocked polyisocyanate compound is used as a crosslinking agent for hydroxyl group bearing polyester resins, however, in this combination, a blocking agent is used which is vaporized at the stage of baking the formed coating, causing troubles in working the coating. Therefore, there is preferred the use of combination of a carboxyl bearing polyester resin and a crosslinking agent selected from glycidyl or oxirane group bearing epoxy resins or compounds, with the exception of toxic triglycidyl isocyanurate. Examples of such crosslinking agents are bifunctional epoxy resins or compounds such as bisphenol type glycidyl ethers, diglycidyl ethers of dialcohols (Japanese Patent Publication (unexamined) 151224/75), diglycidyl terephthalate (Japanese Patent Publication (unexamined) 243176/88) and the like, and polyfunctional epoxy resins or compounds such as aliphatic hydrocarbon glycidyl ethers, novolak type epoxy resins (Japanese Patent Publication (unexamined) 28092/72) and the like. With the increase in demand of coating powder which is specifically suitable for a high-temperature and short time baking as required for the coating of electrical appliances, office supplies or the like, much importance is attached to the use of to trifunctional or more highly functional epoxy resins or compounds to increase the crosslinking density. However, heretofore proposed aliphatic hydrocarbon glycidyl ethers do not give the desired increase in the degree of crosslinking and novolak type epoxy resins, while increasing the crosslinking, inevitably result in a decrease in bending processability and often result in a yellowish coating. Thus, none of the known polyfunctional epoxy resins or compounds satisfy the simultaneous improvement in the degree of crosslinking and bending properties.
It is, therefore, an object of the invention to discover a polyfunctional epoxy resin or compound which is free from dermal toxity is easy to use in operation and which is useful as a crosslinking agent for carboxyl group containing polyester resins, such as to produce a highly crosslinked resin having excellent properties especially bending properties. The principal object of this invention is to provide a coating powder composition comprising such polyfunctional epoxy resin or compound and carboxyl group containing polyester resin, which is suitable for a high temperature and short time baking and capable of resulting in a coating with excellent solvent resistance, impact resistance, bending properties and other mechanical strengths.